Two-step stress tests for Japanese plants

11 July 2011

Japanese reactors shut for periodic inspections would be able to restart after successfully completing the initial step of ‘stress tests’, while all units would be subjected to more comprehensive tests in a second stage.

Last week, prime minister Naoto Kan said that the country's nuclear facilities would be subjected to stress tests before being allowed to restart. However, he was unable to elaborate on what those tests would involve.

Japan's chief cabinet secretary, Yukiyo Edano, has now said that the stress tests would be conducted in two phases. Step one, he said, would be applied to the 35 reactors which have been taken offline for periodic inspections to determine whether they could withstand large earthquakes and tsunamis. Under this step, utilities will be required to examine the safety margin of important pieces of equipment in accordance with guidelines to be set by the country's Nuclear and Industrial Safety Agency (NISA) and Nuclear Safety Commission (NSC). Based on the results of these initial tests, the government will decide whether a reactor shut for inspections can or cannot resume operation.

Quake shakes Fukushima region

Cooling operations at the damaged Fukushima Daiichi plant were uninterrupted by an earthquake of magnitude 7 struck the area just before 10:00am on 10 July, Tokyo Electric Power Co (Tepco) reported.

A tsunami warning was issued by the Japan Meteorological Agency, but this was later lifted. Tepco said that workers at the Fukushima Daiichi plant were moved to higher ground before returning to work. The company said that there was no immediate sign of any further damage to the plant.

According to a Bloomberg report, Tohoku Electric Power Co said that its facilities in the region were undamaged by the quake, including the shutdown Onagawa and Higashidori nuclear power plants.

Step two will involve a comprehensive safety assessment of all reactors and will be conducted to enhance the reliability of safety checks. These tests, Edano said, will be similar to the stress tests proposed by the European Union (EU).

The NSC will design the testing program, which will then be undertaken by the individual utilities. The results of the tests will be checked by NISA, who will then report back to the NSC.

Edano did not disclose a timetable for the tests.

As of today, only 19 of Japan's 54 nuclear power reactors are in operation - including two units that are under test operation (Ohi 1 and Tomari 3), according to data released by the Japan Atomic Industry Forum (JAIF). This represents 17,580 MWe, or 36%, of the country's total nuclear generating capacity of 48,960 MWe. Nineteen units, with a combined generating capacity of 15,618 MWe are not operating as they have been shut for periodic inspection, while another two units have been shut for unplanned inspections or equipment replacement.